In order to install or service an HVAC system, HVAC service personnel must measure the HVAC system refrigerant pressure and from the refrigerant pressure determine the saturated vapor equivalent temperature for the particular refrigerant used in the HVAC system being installed or serviced. In addition, other parameters, such as trend lines for refrigerant pressure, trend lines for saturated vapor equivalent temperature, instantaneous refrigerant pressure bar graph, or super-heat/sub-cool temperature of the refrigerant, may be useful in installing or servicing an HVAC system. Conventionally, the refrigerant pressure is measured with an analog pressure gauge and the saturated vapor equivalent temperature for the refrigerant is determined from the measured refrigerant pressure either by the use of lookup tables or by the use of correlated scales on the face of the analog pressure gauge. Digital pressure gauges have also been used in this field.
A typical analog pressure gauge is mechanical and contains a bourdon tube. The bourdon tube is a mechanical transducer. The bourdon tube is a curved and partially flattened tube that tends to straighten out in proportion to internal pressure within the bourdon tube. The bourdon tube is connected to a series of watch-like gears (pointer gears) that rotate a needle shaft with an attached needle pointer to indicate the pressure on the dial of the analog pressure gauge. When the bourdon tube of the analog pressure gauge is connected to the refrigerant line, the refrigerant pressure within the bourdon tube causes the bourdon tube to straighten out so that the needle, mechanically connected to the bourdon tube through the gears, indicates the refrigerant pressure on the dial of the analog pressure gauge.
A conventional analog refrigerant pressure gauge 11 is shown in FIG. 1. When such an analog pressure gauge 11 is used to service a HVAC system, the main analog scale 13 of the analog pressure gauge 11 indicates pressure in PSI (pounds per square inch) or KPa (metric Kilo-Pascals). Additional inner analog scales (circular bands of numbers) 15 are also printed on the face of the analog pressure gauge 11. The additional inner scales 15 indicate the saturated vapor equivalent temperature for different refrigerants at the measured refrigerant pressure.
Conventional pressure gauges similar to those shown in FIG. 1 require careful calibration in order to obtain an accurate measurement. Specifically, the gauges may become inaccurate over time when they are dropped or banged during handling and moving. In some instances, HVAC technicians forget to calibrate their gauge sets. Regular calibration also can be burdensome on the technician. Additionally, even when the gauge sets are calibrated, there is a possibility that the calibration is not performed accurately. Finally, digital gauges do not include a method by which the technician is able to ascertain whether the gauges have been calibrated or, if so, in a satisfactory manner. Thus, technicians do not have confidence in such gauges and tend to steer clear of digital gauges because they lack confidence in their calibration. Inaccurate gauges lead to unsatisfactory performance of HVAC units and longer times for performing routine repair and maintenance.
It is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.